This invention relates to an apparatus for heating yarn and, more particularly, it relates to a radiantly heated apparatus to assist in drawing yarn to produce products at higher speeds without loss of yarn properties.
A drawing process in which the present invention is useful is disclosed by Good in U.S. Pat. No. 3,311,691. Good discloses a process for drawing a polyamide yarn that comprises the steps of forwarding a substantially undrawn polyamide yarn to a friction element to provide a first drawing by snubbing the said yarn about the said friction element and removing the said yarn from the said friction element at a linear speed of from about 2.2 to about 5.0 times the rate at which the said yarn is supplied to the said friction element, thereafter while further forwarding the said yarn, simultaneously (A) heating the said yarn through a fixed length of yarn path to a temperature of at least 130.degree. C. and less than 10.degree. C. below the melting point of the said polyamide (B) providing a second drawing of the said yarn by removing the said yarn from the said length of yarn path at a linear speed at least about 1:1 times the rate at which the said yarn is supplied to the said length of yarn path, thereafter maintaining the yarn at constant length while heating substantially at the temperature of the said length of yarn path for a period of from about 0.25 to about 0.60 second and finally cooling the said yarn while forwarding to windup at a linear rate of from about 0.985 to about 0.895 times the rate of the said yarn while maintained at constant length.
The purpose of heating the yarn in step (A) is to reduce yarn draw tension by increasing the yarn's temperature. This is accomplished by passing the yarn around a heated tube. Some heating of the yarn occurs due to friction between the yarn and the tube and some yarn heating occurs as a result of drawing of the yarn as the yarn passes around the tube which is an exothermic process. This creates problems in controlling yarn temperature. Control of the yarn temperature at this location is important to the process because uncontrolled variations in temperature can cause poor operability and less than acceptable yarn mechanical quality.